Work holder rack



Alig. 19, 1969 E, CONRAD ET AL 3,461,842

WORK HOLDER RACK Filed NOV. 19, 1965 v I8 I9 I IIIIIIJI {5 INVENTORS ERNEST E. CONRAD ARM!" A. FlNGER 1 ,4 WMM M aya- ATTORNEYS United States Patent 3,461,842 WORK HOLDER RACK Ernest E. Conrad, Clinton Corners, and Armin A. Finger,

Ponghkeepsie, N.Y., assignors to International Business Machines Corporation, Armonk, N.Y., a corporation of New York Filed Nov. 19, 1965, Ser. No. 508,669 Int. Cl. B05c 11/14 US. Cl. 118-500 2 Claims ABSTRACT OF THE DISCLOSURE A tubular stacking device for use in a container of a centrifuge containing a coating liquid and wherein the objects to be coated are placed on circular pans which are inserted and held in a plurality of transverse slots, and wall portions of the device opposite such slots, in the stacking device and which slots contain passageways to permit the escape of gas trapped between the objects when the stacking device is loaded and placed in the container.

This invention is directed generally to an apparatus for simultaneously coating a plurality of objects with particles and, more particularly, to an apparatus for simultaneously coating a plurality of objects with a layer of finely divided particles to form on each object a thin, hole-free film of fused particles thereon.

It is often desirable to deposit particles of a particular substance onto an object to create a new or improved product which has enhanced qualities. In manufacturing cathode ray tubes, for example, it is often desirable to form the screen by depositing fluorescing'powdered material sensitive to electron beam bombardment on the face of a cathode ray tube. The deposited powdered material is generally deposited with a binder substance to adhere the powdered material to the face of the cathode ray tube; however, the binder material can be applied to the powdered material after its deposition on the face of the cathode ray tube.

In many situations it is desirable to deposit particles onto an object and fuse or join the deposited particles to form a coating on or about the object. In the manufacture of various electrical components, such as resistors, capacitors and semiconductor devices, it is often necessary to provide a tightly adherent protective jacket which serves as a hermetic seal and prevents the contamination of the components by foreign or noxious materials which may impair the electrical characteristics of the device or may physically damage them so as to render them unsatisfactory or worthless. A wide variety of coating materials, such as plastic and glass has been employed with some success, and some of these coating materials have been formed by fusing or joining particles deposited on the components.

The present trend in the electronic computer fields is toward the miniaturization of semiconductor or solid state components, i.e., integrated or monolithic circuits. Accordingly, only thin protective coatings are practical since thick protective coatings undesirably increase the bulk of such components, and often such thick jackets are subject to cracking during use over a range of operating temperatures.

Two US. patent applications entitled Method of Forming a Glass Film on an Object and the Product Produced Thereby and Method of Forming a Glass Film on an Object, whose respective serial numbers and filing dates are S.N. 141,668 (now US. Patent No. 3,212,921) and SN. 181,743, (now US. Patent No. 3,212,929) filed Sept. 29, 1961 and Mar. 22, 1962 and assigned to the same assignee of this invention, relate "ice to techniques for forming thin glass film-s on an object for the purpose of providing a hermetic seal or coating therefor. Both of these above-identified applications use centrifuging techniques for depositing glass particles onto the object, and a glass film is then formed on the object by fusing or joining the deposited glass particles.

Thus, the prior art teaches means for coating a single object with a layer of finely divided glass particles by covering the object with a liquid in which is suspended the glass particles and then subjecting the object and suspension to centrifugal force sufiicient to cause the glass particles to be deposited on the object.

However in this prior art, only one object at a time could be coated in each container containing the glass suspension since it was considered necessary to maintain a minimum ratio of 0.6 to 0.7 of height of liquid column over the object to the diameter of the container. If such a minimum ratio were not maintained, the liquid became resonant due to the vibration of the centrifuge, thereby resulting in an unusable deposition of the glass particles on the object.

Therefore, it is an object of this invention to produce an apparatus for simultaneously depositing particles on a plurality of objects by centrifuging.

It is another object of this invention to provide an improved centrifuging apparatus for simultaneously depositing particles on a plurality of objects.

A further object of this invention is to provide an improved apparatus for simultaneously depositing by centrifuging from a liquid suspension glass particles on a plurality of objects wherein the height of liquid over each object is independent of the diameter of the container in which the objects and the suspension are placed.

A more specific object of this invention is to provide an improved apparatus for simultaneously depositing by centrifuging from a liquid suspension particles on a plurality of objects by stacking the objects in a container containing the suspension and maintaining the liquid in the container at a height sufiicient to prevent resonance of the liquid.

A more specific object is to provide an improved apparatus for simultaneously depositing by centrifuging from a liquid suspension particles on a plurality of objects placed in a container of the liquid suspension and maintaining a minimum ratio of liquid height in the container to container diameter of approximately 0.6 to 0.7.

Still another object of this invention is to provide an improved apparatus for simultaneously depositing by centrifuging from a liquid suspension particles onto a plurality of objects which are stacked and held in spaced relationship during centrifuging.

Another object of this invention is to provide an improved apparatus for simultaneously depositing by centrifuging from a liquid suspension particles upon a plurality of spaced objects wherein the spacing of the objects is independent of the ratio of the height of the liquid and the diameter of the container containing the liquid suspension and the stacked objects.

This invention is based on the discovery that a plurality of objects may be coated by stacking them in a liquid suspension in a container and centrifuging without maintaining a minimum ratio of approximately 0.6 to 0.7 of

liquid column in the container is sufficient to maintain the minimum ratio of 0.6 to 0.7. The objects to be coated may be semiconductor wafers, and the particles may be finely divided glass particles in a colloidal suspension.

In accordance with a particular form of the irivention, there is provided a stacker tube having a plurality of spaced transverse slots for receiving carriers containing the wafers to be coated. The loaded stacker tube is placed in a matching container containing a liquid suspension of the glass particles. Several of the loaded containers may then be placed in a single centrifuge cup and subjected to a centrifuging operation.

The foregoing and other objects, features and advantages of the invention will be apparent from the following more particular description of a preferred embodiment of the invention, as illustrated in the accompanying drawing.

In the drawing:

FIGURE 1 is a perspective view in partial section of a stacking device embodying the principles of this invention for holding a plurality of objects simultaneously to be coated by centrifuging.

FIGURE 2 is a separated sectional view of a stacking device of FIGURE 1.

FIGURE 3 is a diagrammatic representation of a centrifuging apparatus employed in depositing glass particles on objects stacked in devices of the type illustrated in FIGURE 1.

FIGURE 4 is a perspective view of a prior art container for holding a single object to be coated by centrifuging.

In FIGURE 1, there is shown a stacking device consisting of a stacker tube 11 placed in an outer tube or container 12 which contains a colloidal suspension of very fine glass particles. The outer diameter of tube 11 is only slightly less than the inner diameter of container 12. The surface of the liquid suspension is designated by the reference numeral 13. The method and materials used in producing this liquid suspension are set forth in the two pending applications cited above and another pending US. application entitled Method and Apparatus for Depositing Particles onto an Object, S.N. 437,805, filed Mar. 8, 1965, now Patent No. 3,406,041 and assigned to the assignee of this invention.

Eight vertically spaced slots 14 are formed in the wall of stacker tube 11. Each slot extends half way or slightly more around the periphery of tube 11. As shown in more detail in FIGURE 2, the inner surface of stacker tube 11 is undercut at the lower surface 15 of each slot 14 to form a shoulder 16. Each slot 14 and shoulder 16 continues as a recess 17 in the other half of the inner wall of stacker tube 11. The depth of this recess is the same as the depth of the undercut to form shoulder 16. The height of the recess is the height measured between the upper surface of shoulder 16 and the top of 18 of the corresponding slot.

A hole 19 is cut through the wall of stacker tube 11 in approximately the center of each slot 14. A hole 20 is also cut through the stacker tube wall in approximately the center of each recess 17.

The structure of stacker tube 11 just described is for the purpose of receiving in each slot 14 a pan 21 carrying a semiconductor wafer 22 which is to be coated by the deposition thereon of glass particles from the liquid suspension in container 12. Pan 21 has a lip or flange 23 extending around the top thereof. The height of pan 21 is slightly less than the height of each of the slots 14 so that a pan may be inserted in each slot. The diameter of lip 23 is approximately the same or slightly less than the diameter of the inner wall stacker tube 11 measured between the recess 17 and the undercut portion of each slot 14.

In practicing the invention, the stacker tube 11 is removed from container 12 by means of a detachable handle 24 which grasps the top of stacker tube 11. Container 12 is then filled with a liquid suspension of finely divided glass particles which are to be deposited on a plurality of objects, such as wafers 22. Each slot 14 is then loaded with a pan 21 carrying a wafer 22. The upper slot 14 in FIGURE 2 is shown with a pan 21 in place. The pan is inserted through the slot by holding the pan either with the fingers or tweezers. One function of each of the holes 19 is to permit the pan conveniently to be inserted in the corresponding slot 14. The lip or flange 23 of each pan 21 rests upon the shoulder 16 which extends completely around the inner periphery of stacker tube 11 except for the holes 19 and 20.

The loaded stacker tube 11 is then lowered into container 12 containing the liquid suspension. As the stacker tube is loaded into the container the air trapped between the pans 21 is permitted to escape through the holes 19 and 20 to the surface of the liquid. The upper half of each hole is above, and the lower half below, the inserted pan. With stacker tube 11 in place within the container 12, the height of the liquid must be such that resonance will not occur during the subsequent centrifuging operation. Resonance will not occur if a minimum ratio of 0.6 to 0.7 of liquid height to container diameter is maintained.

A typical centrifuge 25 is shown in FIGURE 4. An electric motor 26 rotates at a very high speed a plurality of centrifuge cups such as 27, 28 and 29. At this high speed, the centrifugal force causes the cups to assume a hori- Zontal position as indicated by the dashed lines. The centrifuging operation necessary to deposit glass particles from the liquid suspension onto each of the wafers 22 is ordinarily conducted for one to two minutes at a speed suflicient to develop a centrifugal force of 1000- 2500 g. The centrifuging time and speed are not critical. Slow speeds ordinarily require a longer time to deposit glass particles on the object or substrate. Speeds sufficient to develop centrifugal forces of about 1870-2500 g. have proved to be particularly desirable in depositing particles of glass. Greater details of the centrifuging operation are presented in the three pending applications cited above.

Several of the stacking devices 10 may be placed in each of the centrifuge cups of centrifuge 25. During the centrifuging operation then, for the preferred embodiment shown, eight times as many wafers 22 may be coated at the same time in one container than was possible with the prior art method. A typical prior art device is shown in FIGURE 3. This device 30 consists of a container 31 containing a liquid suspension of glass particles. The upper surface of the liquid suspension is designated by the reference numeral 32. Placed in the bottom of container 30 is a single wafer 33. The liquid height in container 30 must be maintained at a sufficiently high level such that the height of the surface 32 above wafer 33 is related to the diameter of the container 30 by a minimum ratio of 0.6 to 0.7, thereby preventing resonance during centrifugmg.

Therefore, it is seen that this improved apparatus permits a plurality of wafers to be coated in a single container by stacking them in spaced vertical relationship in a stacking device such as stacker tube 11. This improved apparatus is based upon the discovery that the minimum liquid height to container diameter ratio of 0.6 to 0.7 need not be maintained relative to each wafer in the stack. but rather only the total height of the liquid in the container need be related to the container diameter by the minimum ratio. Consequently, the height of the liquid above each individual wafer is independent of the container diameter, and also the spacing between the stacked wafers is independent of the container diameter so long as the total height of the liquid suspension in the container is sufiicient to maintain a liquid height to container diameter minimum ratio of approximately 0.6 to 0.7, thereby preventing the occurrence liquid resonance during the high speed centrifuging operation.

While the invention has been particularly shown and described with reference to a preferred embodiment there- 5 of, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention.

What is claimed is:

1. A stacking device for use in the cylindrical container of a centrifuge for simultaneously coating with a film of particles a plurality of objects placed in a liquid suspension of the particles in said container, said stacking device comprising a hollow cylinder having a plurality of spaced slots disposed transverse to the longitudinal axis of said cylinder for receiving and supporting a plurality of cylindrical pans containing the objects to be coated, and wherein each said slot extends around one-half of the periphery of said cylinder and continues as only a recess around the other half of the inner wall of said cylinder, and wherein each recess has a hole formed through the wall thereof to permit the escape of gas trapped between the objects when said stacking device is loaded with objects and place in said container.

2. A stacking device as defined in claim 8 wherein each slot is widened in a portion thereof to permit the escape of gas trapped between said objects.

References Cited UNITED STATES PATENTS 689,213 12/ 1901 Nicholson. 3,207,127 9/ 1965 Smith 118-503 X 3,226,254 12/ 1965 Reuschel 118--503 X 3,168,100 2/1965 Rich 118500 X 3,069,213 12/ 1962 Azzarri 31210 FOREIGN PATENTS 692,996 6/ 1940 Germany. 950,052 2/ 1964 Great Britain.

MORR KAPLAN, Primary Examiner US. Cl. X.R. 211--41; 23326 

